home Educational literature radiation selection. radiation mutagenesis. Dose-effect patterns Chemical and radioactive mutagenesis

radiation selection. radiation mutagenesis. Dose-effect patterns Chemical and radioactive mutagenesis

Lecture 12

SPONTANEOUS AND INDUCED MUTAGENESIS

There are two types of mutagenesis depending on the nature of this phenomenon. One is determined by the complexity of biochemical and molecular biological processes in the cell, the other is determined by the external factors of the environment in which the organism develops and performs vital functions.

PRE-MUTATIONAL CHANGES IN GENETIC MATERIAL

The patterns of variability are still not well understood. Often we do not know when and in which gene a mutation will occur, which trait will be changed, whether the mutation will be harmful or beneficial to the organism.

On the other hand, let's remember from a biochemistry course that cells have a special enzymatic repair system that corrects replication errors and thus reduces the error rate to 10–8 – 10–10. However, taking into account the characteristics of organisms, we can say that the larger the genome, the potentially greater number of spontaneous or induced mutations can be formed in it. It was shown that mutagenesis occurs even in dry seeds and dormant cells, which may be due to the fact that the DNA of such biosystems is in the A form.

Speaking of pre-mutational changes, it should be remembered that they are actually mutations that exist for a limited time, during which the repair enzymes have time to correct them. And only a small part of such changes turns into true mutations. The action of an additional factor (even non-mutagenic, for example, temperature) can lead to an increase in the number of observed mutations, since this factor disrupts the work of repair enzymes. Such a phenomenon has been shown, for example, for the Drosophila fly, in which the number of mutations increased significantly if, after irradiation, x-rays they were further exposed to elevated temperatures. The phenomenon is called the EFFECT EFFECT. At the same time, one should not forget that mutations appear in subsequent generations.

In conclusion, it should be noted that although the study of mutagenesis by the methods of genetic engineering is a major step, it does not at all eliminate the need to study the regularities of the mutation process at the level of a cell or a whole organism.

In the previous topic, we talked about the fact that mutations are based on changes in nucleotides, and the mutation process in different parts of chromosomes (DNA) can proceed at different rates, which largely depends on the presence of methylated nitrogenous bases there. Considering the mutation process in relation to whole organisms, it should be said that for each species of animal, plant or bacterium, the frequency of occurrence of mutations and the direction of mutation are different. These differences are due to the influence of many factors: the genotypic features of the species, the degree of its adaptation to environmental conditions, the strength of natural factors, etc.

For example, when studying the mutation process in Drosophila, it was found that in the whole organism, taking into account visible, as well as various small mutations, it turns out that about 5% of gametes acquire new mutations in each generation. With regard to individual chromosomes, it was found that mutations of a lethal nature occur in the sex X chromosome with a frequency of 0.15% per generation, and the occurrence of mutations in the second chromosome occurs with a frequency of about 0.5%.

Different mutability of individual genes was also revealed. For example, in corn, this indicator for the aleurone red color gene is 1.1 per 100 thousand gametes, and for the gene that provides the synthesis of the anthocyanin pigment, it is 182 per 100 thousand gametes.

It has been observed that similar genes in different genotypes mutate at different rates.

The accumulated experimental material suggests that spontaneous gene mutation to a certain extent depends on physiological and biochemical changes in the cell caused by external factors. At the same time, the appearance of natural (spontaneous) mutations in microorganisms does not at all require contact of the cell with the factor in relation to which mutations can appear that provide their adaptive reactions.

Spontaneous mutations in humans are widely represented. So, for 1 million gametes formed, there are about 400 carrying mutations for thalassemia, 70 for chondrodystrophy, 28 for albinism and color blindness, and 32 for hemophilia.

The factors of the natural mutation process should include not only errors in the process of replication, transcription and translation, but also those that can be caused by changes in the physiological and biochemical processes in the cell (for example, increased formation of hydrogen peroxide or other substances of a similar effect). At the same time, environmental factors seem to be the BASIS for the appearance of natural mutations.

Until recently, the dominant role in this process was assigned to the natural radiation background, which consists of cosmic rays, terrestrial radiation and the action of radioactive isotopes that enter the body from the outside, incl. with food (eg Ra, 40 K, etc.). The value of this background is 0.12-0.23 rad per year.

The effect of radiation on organisms with short life cycles may be small. But in humans, during ontogenesis, up to 25% of the total number of mutations can occur precisely under the influence of the natural radioactive background. Plants living up to a thousand years or more (for example, sequoias) may be even more affected by this factor.

The study of the described problem led to the discovery of specific substances - antimutagens, providing a kind of protection of organisms from this factor, as well as other mechanisms associated with the regulation of the mutation process as a whole. First of all, this is the discovery of mutator genes that increase the mutagenic process in certain regions of chromosomes by 1-2 thousand times, which is partly due to a change in the mechanism of action of one of the central enzymes of DNA replication - DNA polymerase. Also shown is the functioning of the antimutator gene, which regulates the activity of the specified enzyme, and thereby reduces the number of mutations that occur during replication. Similar mechanisms of action of the described genes have also been shown for other proteins and enzymes involved in the DNA replication process: DNA ligase, DNA-binding proteins, and other proteins.

It was also found that the formation of mutations can be genetically blocked in the same way as any other physiological process. For example, a change in the lex A or rec A genes in the bacterium E. coli leads to partial or complete suppression of the mutation process under the influence of ionizing radiation, ultraviolet light, or some chemical mutagens.

INDUCED MUTAGENESIS

Under the induced mutational process is understood the occurrence of hereditary changes under the influence of the directed influence of factors of the external or internal environment. Changes are the result of complex physiological processes of the cell, which are based on chemical and physico-chemical reactions.

The first results in this direction were obtained at the beginning of the 20th century. At the same time, the greatest success was achieved in studying the effect of ionizing radiation, which were the main objects of research by physicists of that time.

The discovery by Nadson and Filippov in 1925 of the mutagenic action of radium rays during their treatment of yeast cells began the era of induced mutagenesis. However, the American researcher Möller is considered the founder of this scientific direction, who was the first to carry out a quantitative account of mutations of this type in Drosophila and thus laid the foundation for radiation genetics as a new scientific direction.

A significant number of studies on various objects have led to the development of theoretical ideas about the mechanism of the biological effect of radiation injury. Grauter introduced the concept of a target - a "sensitive" cell volume, the defeat of which is responsible for changing a certain reaction in the cell. Quantitative analysis of mutagenic effects under the action of various doses of radiation made it possible to reveal some regularities.

In the simplest case, when one target is responsible for the observed reaction in the cell, and one hit is required to destroy it, the number of affected cells grows exponentially with increasing dose. The single-impact curve equation is described by the formula:

N / N o \u003d 1 - e  D,

where N o - total number cells, N is the number of inactivated (dead) cells, e is the base of the natural logarithm inactivation probability per 1 cell, D is the radiation dose.

With a one-hit mechanism, the number of mutations is directly proportional to the dose:

If several hits are needed to hit the target, then an S-shaped curve is obtained:

The study of the impact of different types of radiation showed their unequal effectiveness. The presence of a charge, mass and energy characteristics of an electron, proton, photon and other particles determine their different effects on the cell, as well as the magnitude of the effect produced at the same dose of radiation. It also turned out that for different organisms, tissues and different types of mutations, the genetic efficiency of these types of radiation can be different and differ by tens or even hundreds of times.

The presence of oxygen in the environment at the time of cell learning enhances the mutagenic effect, so the concept of the oxygen effect of radiation has been introduced. Temperature, infrared or ultraviolet irradiation of an object can have a similar effect. In this case, the effects of exposure may be different depending on whether the factor acts before irradiation, during it, or after irradiation. The presence of water (which is shown on seeds of different humidity), the presence of chemical reagents (formaldehyde, heavy metals, etc.) also sharply modifies the effect of exposure to radiation. In humans, such factors can be the presence in the body of certain drugs or protective substances (for example, of an antioxidant nature).

The internal factors of the body are also reflected in the magnitude of the genetic effect of radiation. First of all, this is due to the phase of the cell cycle, when the same dose of radiation has a different effect even in different phases of meiosis, which was shown in the study of gametogenesis in wheat.

When characterizing radiation sources, the concept of dose is used. The dose of x-rays and  rays is measured in roentgens. One roentgen is such a dose of radiation at which in 1 cm 3 of air at n.o. (0 o C and 1 atm.) 2 billion pairs of ions are formed. The formation of one pair of ions requires an energy of 34 eV.

The dose rate is measured in roentgens per unit time (min., hour), because. it is clear what more time the radiation lasts, the greater the effect it can produce.

The literature also uses other concepts that reflect the presence of an object under irradiation conditions. Therefore, the units of the absorbed dose of radiation by an object are measured in Grays (Gy) for any period of time:

1 x-ray \u003d 1 rad \u003d 0.01 Gray.

The absorbed dose rate by objects is measured in sieverts (Sv), which makes it possible to take into account the location of an object in areas with different levels of radiation and for different periods of time over a certain period:

1 r / s \u003d 1 REM (roentgen equivalent) \u003d 0.01 Sv.

The data are summarized and the total dose of radiation received by the object over any period of time is determined. At the same time, there are regulatory documents that determine the limiting values of exposure for each organism. So for a soldier in a combat situation, a dose of 50 r per month is considered relatively harmless. It does not matter whether it is received in 1 hour or in small doses within a month.

The biological effectiveness of exposure to radiation can even be calculated theoretically. So, in order to break a chromosome thread 0.1 microns thick, 15-20 ionizations are necessary, which is equivalent to an irradiation dose of 80-100 roentgens.

To characterize the degree of soil contamination with radioactive substances, the concept of soil contamination density is used, which is expressed in units - Curie (Cu, Ku) per 1 km 2 and corresponds to a certain radiation dose rate:

1 Ku / km 2 \u003d 1 microdistrict / hour.

ABOUT RELATIVE BIOLOGICAL EFFICIENCY (RBE)

DIFFERENT TYPES OF RADIATION

The RBE of one type of radiation to another is defined as the ratio of the corresponding doses that cause the same biological effect. The efficiency of radiation largely depends on the rate of linear energy loss inherent in each type of radiation.

Relative genetic efficiency depends to a large extent on a variety of conditions at the time of irradiation or even after it, as discussed above. For example, the RBE of fast neutrons and X-rays per chromosome in mouse cells in an oxygen atmosphere was 2.5 to 1, and when irradiated in a nitrogen atmosphere, it was 6 to 1.

In experiments on horse bean cells, it was found that damage to chromosomes by neutrons and -rays is approximately 10.5 to 1, and in the absence of oxygen - 18 to 1. On another plant, tradescantia, it was shown that the RBE of radiation can reach 100 to 1.

It has been shown in human cell culture that, at all phases of the cell cycle, X-rays cause 1.5 times more chromosomal rearrangements than -rays alone.

THE PROBLEM OF THE THRESHOLD OF THE MINIMUM

RADIATION AND LOW DOSES OF RADIATION

Identified by Möller linear dependence lethal, sex-linked mutations in Drosophila led to the question of the threshold problem; the minimum level of radiation that is believed to be safe for organisms.

Spencer and Stern (1948) showed that the natural mutation process in Drosophila produces 1 mutation per 1,000 gametes. A radiation dose of 50 roentgens doubles this value. The linear dependence of the further results of the experiment indicated the absence of a minimum dose threshold.

The presence of natural background radiation and environmental pollution with radionuclides due to an increase in the content of protons, for example, the 40 K isotope due to the use of fertilizers or accidents like Chernobyl, or due to other reasons, incl. the use of radioactive substances in industry or in military affairs, force a more thorough study of the problem of minimum radiation doses for living beings, resulting in various genetic effects that are harmful to the life of organisms.

Biochemical studies have shown that in the cell there are special enzymatic systems for the repair of hereditary material for cases of violations in the genetic material that occur at a certain speed. With the constant active work of such a system, mutations occur at a rate of 10–8–10–9 nucleotides per one cell division, which is the basis of spontaneous mutagenesis. Therefore, even the minimum dose of irradiation of the organism only adds to the number of disorders in the genetic material, and even with the activation of the damage repair system, the total yield of mutations will be higher than under normal conditions.

When we turn to the concept of radiation dose rate, i.e. If we take into account the time factor, it turns out that genetic effects appear in any case, and this does not depend on the action of low or high doses. On the one hand, this is due to the absence of a lower threshold of radiation, and, on the other hand, the principle of cumulation (accumulation) of genetic effects due to the action of small doses is observed, since mutations are persistent changes in chromosomes. Therefore, the radiation effect can phenotypically appear earlier when a certain dose is taken in a short time, or later if the absorbed dose is taken over a long period of time.

Thus, high and low doses of radiation differ in this aspect only in terms of mutability levels per unit of exposure. However, the genetic effects of exposure to different doses of radiation can vary by a few percent, several times, or even tens and hundreds of times, depending on the type of irradiated tissue, the species of the organism, and its physiological state.

Cytological studies mechanism of chromosomal rearrangements also made it possible to prove that with an increase in the radiation dose, the number of violations in the structure of chromosomes (the so-called aberrations, including fragmentations and deletions) increases.

THE PHENOMENON OF MAXIMUM MUTATIONS

The study of the problem of the growth of mutations with an increase in the dose of irradiation of the object led to the question of whether there is any limit to the maximum number of possible mutations. At the same time, it was also found that the greater the energy of the particles and the energy loss during the movement of particles through the object, the higher the value of the relative biological efficiency of the radiation. However, as it turned out, there comes a moment when the energy of the particles is so high that part of their energy is no longer used, and the RBE of radiation begins to decrease. In general, the dependence of the number of mutations on the amount of irradiation has a complex character: at first it grows, reaches a plateau, and at high doses, the number of mutations (per surviving cells) decreases.

This phenomenon has been called the phenomenon of maximum doses.

Here, some clarifications should be made, since in the experiments there was an overlap between the fact of accumulation of mutations and the number of cells that died after irradiation. The explanation boils down to the fact that at first there is an accumulation of mutations, after which, with a further increase in the dose, the most radiosensitive cells die, while the radioresistant ones continue to perform their functions. In the end, there are very few of them left, i.e. the size of the target for exposure to radiation is significantly reduced, which leads to a decrease in the observed effect.

Cytological and biochemical studies have shown that at low doses of radiation, mainly point mutations occur (changes in individual nucleotides), and the number of intragenic deletions (loss of small DNA sections) is proportional to the square of the dose.

MUTAGENIC EFFECT OF ULTRAVIOLET

The problem of the mutagenic effect of ultraviolet rays has attracted the attention of the general public in connection with studies of the Earth's ozone layer. The discovery of ozone "holes", their variability in size and location above our planet, on the one hand, and the expansion of opportunities for recreation in the mountains and on the sea coast, on the other hand, have significantly increased the relevance of studying the effect of ultraviolet radiation on the vital activity of organisms.

Researchers divide the ultraviolet spectrum into three areas: UV-C - hard ultraviolet with wavelengths less than 280 nm, UV-B - medium with wavelengths in the range of 280-320 nm and UV-A with wavelengths of 320-340 nm. The spectrum of "hard" ultraviolet is absorbed by the Earth's atmosphere and does not reach its surface. "Medium" ultraviolet can penetrate not only through the ozone "holes", but also when the ozone layer is thinning, which is caused both by natural causes and, apparently, by anthropogenic activity. UV-A is not thought to be harmful to organisms.

Microorganisms are most susceptible to the mutagenic (and usually harmful) effects of UV-B, since these rays easily reach their nuclei with hereditary material. It has also been shown that ultraviolet has a mutagenic effect on all other organisms if it reaches the generative tissue or germ cells (eg, in plants). At the same time, the appearance of somatic mutations that are not hereditary in nature, but cause changes in the functioning of cells and tissues, which affects the vital activity of organisms, is shown.

It has been shown that ultraviolet light is capable of inducing all types of mutations, the frequency of which depends on the radiation dose and dose rate. Ultraviolet with wavelengths of 250-280 nm has the highest efficiency, which is explained by the maximum ability of DNA to absorb light with a wavelength in the region of 260 nm (due to the structure of nitrogenous bases). That is why such ultraviolet effectively destroys DNA molecules, which explains the high sensitivity of cell nuclei.

The mechanism of action is associated with the formation of dimers, mainly thymine, as well as cytosine, uridine, and even between T and C. All this leads to impaired DNA functions, not only regarding transcription, but also the replication process.

Another mechanism of action of ultraviolet radiation is that when it is exposed to the aquatic environment of the cell, hydrogen peroxide (H 2 O 2) and organic peroxides are formed, which also have a mutagenic effect on the hereditary material of the cell. For example, experiments on E. coli showed that when it is grown on a medium pre-irradiated with ultraviolet light, the frequency of mutations in cells increases by 50-100 times. A decrease in the oxygen content when growing Escherichia coli on a pre-irradiated medium or a decrease in oxygen concentration during irradiation of the medium significantly reduces the formation of peroxides and the frequency of mutations in the microorganism.

The visible spectrum of light (photoreactivation) has a protective effect against exposure to ultraviolet radiation, and its ability to suppress the mutagenic effect of ultraviolet radiation has been experimentally proven. Visible light is also able to partially suppress the action of ionizing radiation, since it stimulates the activity of enzymes that reduce the concentration of various peroxides. These enzymes include, for example, catalases and cytochrome oxidases.

The efficiency of photoreactivation also depends on other factors: the pH of the medium, temperature, the physiological state of the cell, and the characteristics of the genotype.

CHEMICAL MUTAGENESIS

The mutagenic effect of chemical compounds was discovered in the middle of the twentieth century. On the larvae of one line of the Drosophila fly, it was shown that formaldehyde induced the appearance of lethal mutations in about 6% of cases. Further, the mutagenic effect of mustard gas, a poisonous substance used during the First World War, was revealed. At the same time, it was shown that chemicals can cause not only all types of point mutations, but also chromosomal rearrangements.

To date, quite a few substances are known to have this property. At the same time, the use of a particular substance is determined primarily by the purpose of the experiment. At the same time, the mutagenicity of a chemical compound is determined, firstly, by the possibility of its penetration into the cell while maintaining its viability and, secondly, by the ability to reach the cell nucleus, affect the structure and / or functions of chromosomes, and others. chemical processes in a cage.

You should also take into account the dosage, the state of aggregation of the substance, the features of the object of study, the stage of development of the organism, and for germ cells - the stage of gametogenesis. Sometimes the mutagenic effect of a substance can manifest itself only with a certain method of its introduction into the body. So, if formaldehyde was used as a food additive for Drosophila fly larvae, then its mutagenic effect was found. In experiments with the effect of vapors of this substance on larvae or adults, the mutagenic effect of formaldehyde was not manifested.

A large number of chemical mutagens gives rise to attempts to classify them either by chemical structure or by the effect of action.

So, N.P. Dubinin distinguishes 9 main classes of chemical mutagens, among which he notes:

alkylating compounds;

peroxides;

aldehydes;

salts of heavy metals;

analogues of DNA bases;

dyes

According to the chemical action, the following groups of substances are distinguished:

radiomimetic, since their mutagenic action is similar to that of ionizing radiation (eg, formaldehyde, ethyl methanesulfonate, etc.);

peroxides, the active components of which are -OH, -H, HO 2 - radicals, formed from peroxides under the influence of such factors as oxygen, water, ultraviolet, visible light;

metabolite analogues, the mechanism of action of which is to compete with conventional metabolites and replace them. These are, for example, derivatives of purine and pyrimidine bases - bromuracil, aminopurine, as well as derivatives of vitamins, for example, folic acid, etc.;

insufficiently studied substances, the mechanism of action of which is not entirely clear.

In conclusion, it should also be emphasized that ionizing radiation, ultraviolet and chemical mutagens cause the formation of mutations that are most fully manifested in the second generation zygote if they occurred in generative cells. This phenomenon is called the phenomenon of delayed mutations.

COMPLEX ACTION OF EXTERNAL FACTORS

Study of the influence of individual environmental factors on hereditary variability reveals only some aspects of their influence on the mutation process. A much more complex picture for interpretation is presented by the results of the combined effects of several factors at once, which usually takes place in nature. Therefore, to assess the contribution of each of the factors, special experiments are set up in such a way that in one series of experiments only one of the factors varies within relatively wide limits, while the others remain approximately at the same level. The results obtained are processed using special statistical methods that allow us to evaluate the contribution of each of the factors individually to the mutation process.

For example, in experiments on Arabidopsis, the interaction of ultraviolet and visible light on the mutation process in a number of genetic forms of this plant was studied. As an estimated characteristic, an indicator was used - the survival of plants. In the experiments, the power and duration of ultraviolet radiation, as well as the restorative properties of visible light, were varied. It was found that the resistance of plants to the harmful effects of ultraviolet radiation is determined by 22% by the characteristics of the genotype and by 18% by the intensity of visible light (PAR - photosynthetically active radiation).

Such experiments are of particular importance in terms of predicting the consequences caused by the impact of factors on biocenoses, for which theoretical models can be built based on the results obtained. This makes it possible not only to foresee negative events in the cenosis, but most importantly, it will allow formulating real ways to prevent them in order to preserve the Earth's biosphere as a whole or its individual components.

USING MUTAGENESIS FOR SELECTION

The discovery of artificial (induced) mutagenesis found practical application in breeding somewhat later (since the 1950s), when some mechanisms of this process became clear and methods for selecting mutants were developed. Obtaining radiation and chemical mutants of agricultural plants made it possible to obtain valuable varieties with a whole range of positive properties: resistance to lodging, diseases, low temperatures, increased economic productivity, etc.

Induced mutagenesis has acquired particular importance in the selection of microorganisms. In fact, the entire microbiological industry for the production of antibiotics, amino acids, vitamins, etc. built on the use of radiation, chemical and "ultraviolet" mutants.

Important mutants have been obtained from the silkworm, which produces natural silk.

radiation mutagenesis- radiation mutagenesis.

Obtaining mutations under the influence of ionizing radiation<ionizing radiation>; distinguish spontaneous (natural) R.m.- under the influence of solar (cosmic) radiation or radiation not controlled by humans (underground fossils, etc.), and artificial (induced, directed) R.m. in human controlled(usually experimental) conditions; second type R.m. is widely used in breeding (especially in plant breeding) to obtain a wide range of different mutations, among which useful ones can be selected.

(Source: English-Russian dictionary genetic terms. Arefiev V.A., Lisovenko L.A., Moscow: VNIRO Publishing House, 1995)

"radiation mutagenesis" in books

Greenhouse effect and radiation afterburner of the atmosphere

From the book Protocols of the Kyoto wise men. Myth about global warming author Pozdyshev Vasily Anatolievich

Greenhouse effect and radiation afterburner of the atmosphere Atmosphere for our planet - how a warm blanket or, rather, as a thermoregulatory suit. Without it, the temperature on Earth would be on average 30 (!) degrees lower, that is, minus 15 degrees Celsius, and also with a huge

radiation apocalypse

From the book Landfills of Death? Made in USSR author Balandin Rudolf Konstantinovich

Radiation Apocalypse Radiophobia is a most dangerous disease. And it was stubbornly spread and exacerbated in our society for many years after the Chernobyl accident. True, at first Gorbachev and his team decided to keep silent. They did not cancel the May Day demonstrations in Ukrainal and

Artificial mutagenesis of the Holocaust symbol

From the book The Genesis of the Holocaust Symbol and the Future of the State of Israel author Vasilyevich Prudnik Alexander

Artificial mutagenesis of the "Holocaust" symbol There are several methods of artificial mutagenesis of intellectual symbols. Artificial mutagenesis of an intellectual symbol is carried out both within the framework of giving the symbol an expansive interpretation, which

What radiation background is called natural?

From book latest book facts. Volume 3 [Physics, chemistry and technology. History and archeology. Miscellaneous] author Kondrashov Anatoly Pavlovich

What radiation background is called natural? The radiation background is called ionizing radiation, due to the combined action of natural (natural) and man-made radiation factors. The natural radiation background is the radiation created by

3.7.1. Mutagens, mutagenesis

From the book Biology [ Complete reference to prepare for the exam] author Lerner Georgy Isaakovich

3.7.1. Mutagens, Mutagenesis Mutagens are physical or chemical factors, the influence of which on the body can lead to a change in its hereditary characteristics. These factors include x-rays and gamma rays, radionuclides, heavy metal oxides, certain

Mutagenesis

From the book Great Soviet Encyclopedia (MU) of the author TSB

Radiation balance

TSB

Radiation capture

From the book Great Soviet Encyclopedia (RA) of the author TSB

Radiation circuit

From the book Great Soviet Encyclopedia (RA) of the author TSB

Radiation pyrometer

From the book Great Soviet Encyclopedia (RA) of the author TSB

Back in 1935, A.N. Lutkov is the closest colleague of the well-known in our country

not a geneticist G.D. Karpechenko- published the article "Mutations and their importance for selection". In it, the author summed up the results of long discussions among biologists and geneticists about the role of mutations in evolution and selection and summarized the facts accumulated by that time on the experimental production of mutations in plants.

The article was based on the work of a famous American geneticist Hermann Möller (Nobe-

Lev Prize in Physiology or Medicine, 1946)), who experimentally proved the possibility of artificial mutations under the action of

by X-rays (1927) and the work of researchers from many countries that followed this discovery to obtain mutational changes with

G. Möller (1890-1967) the power of influence on the plant genome by various physical and chemical factors.

From the post-war period until the mid-1960s, work with experimental mutations in our country was practically not carried out due to an administrative ban on classical genetics, which was officially recognized as pseudoscience.

Mutagenesis made it possible to create large collections mutant plants has opened up new possibilities for solving many fundamental problems of plant biology. For example, thanks to the creation of a collection of chlorophyll mutations, the main stages of chlorophyll synthesis and the main pathways of photosynthetic reactions were studied. Significant progress has also been made in practical selection. For 20-25 years of intensive work in the field of experimental mutagenesis in former USSR several hundred plant varieties have been created using mutant genes. Meanwhile, with the help of induced mutations, only

not big number varieties in the main agricultural plants - cereals,

vegetable and fruit.

The method of experimental mutagenesis has been used more successfully in ornamental floriculture and horticulture to obtain original plant forms. Of course, the mutagenesis method could not completely replace traditional methods selection based on hybridization, recombination and selection, or compete with them, but it was extremely important for the development general theory genetics and plant breeding and added to the arsenal of methods for improving cultivated plants(Maletsky S.I., 2002).

According to B.N. Annenkova and E.V. Yudintseva (1991), radiation mutagenesis has now become one of the progressive methods for obtaining various genetic mutations for subsequent selection and breeding of new varieties. It allows you to obtain forms that have increased productivity, resistance to diseases and adverse environmental factors, an increased yield of biologically active and nutrients in the crop. More than 150 varieties of various agricultural crops have already been obtained in the world with the use of ionizing radiation. For example, high-yielding and lodging-resistant wheat Novosibirsk 67, wilt-resistant cotton variety AN-402 and etc.

Irradiation with gamma rays and neutrons most often affects the seeds or pollen of plants. In this case, the mutation frequency increases by more than 200 times. Mutations affect productivity, precocity, drought and winter hardiness, the size of the plants themselves, and a number of other traits.

The vast majority of the resulting mutants are dominated by oppressed non-viable individuals. Therefore, at the second stage, on the basis of selected forms with improved breeding traits, further breeding is carried out to develop, test, generate and introduce a new variety into practice.

The value of radiation mutagenesis used in plant breeding also lies in the fact that among the mutants there appear forms with new features not found in nature. In this case, the nature and number of mutants obtained are largely determined by the state of the initial material and, in particular, the initial variety.

Relatively young varieties and complex hybrid forms turned out to be the most mutable. Old varieties are very resistant. In addition, the yield and quality of mutations depend on the state of the genome at the time of irradiation and in the post-radiation period of the final formation of the mutation. The genome is understood as the totality of genes contained in the haploid set of chromosomes of a given cell.

Radiation genetics often uses the method of irradiating dormant air-dry seeds. In this case, the quantity and quality of mutations are affected by the conditions of storage and germination of seeds. As a rule, at low humidity, variability increases. The same happens when immature seeds are irradiated. Thus, upon irradiation of immature pea seeds with a dose of 5 kR, the number of mutants increased by a factor of 3 compared with the irradiation of fully ripe ones.

The amount of mutagenesis is also affected by the growing season. It has been established that during the irradiation of legumes, the largest number of economically valuable mutations is obtained in the budding phase.

The formation of mutations depends on the conditions of the irradiation itself: dose, power and type of ionizing radiation. The probability of mutagenesis increases with an increase in the absorbed dose, however, in this case, most of the plants die in the population, and as a result, most of the mutations are not detected. At a high dose rate of irradiation, a high yield of mutations is observed, while at a low dose during irradiation, the plant has time to undergo repair processes.

In practice, various types of radiation are more often used, both with low (X-ray and gamma) and with high ionization density (neutron). At the same time, the former affect the chromosomal apparatus to a lesser extent.

rat, and the latter cause serious disturbances in it that cannot be repaired.

As a result, the spectrum of emerging mutations also changes. Thus, neutron irradiation causes the appearance of a large number of short-stemmed forms with a dense spike in wheat and rye. And irradiation with X-rays and gamma rays causes an increase in resistance to a number of diseases in the obtained forms. At high doses, fast neutrons increase the frequency of chlorophyll mutations in the second generation in comparison with X-rays by tens of times.

The conditions for growing plants from irradiated seeds make it possible not only to increase the level of variability, but also to shift the range of resulting mutations. Among these factors are temperature, daylight hours, root nutrition conditions, and soil and climatic conditions. With a sharp fluctuation of these factors, variability increases.

The method of radiation mutagenesis can significantly reduce the time of breeding a particular variety. Only this selection technique is inherent in the ability to change any one trait that needs correction without changing the whole complex of positive properties and qualities.

It is now generally accepted that deoxyribonucleic acid, DNA, in which four bases - thymine, adenine, cytosine, guanine, are located in a certain sequence, is responsible for the transmission of the organism's hereditary traits. According to this theory, a change in the sequence of these bases in the DNA molecule - the so-called code or their chemical structure will lead to a change in the heredity of the organism.

As a result of experiments carried out by many authors, it was found that when a cell is exposed to reagents - chemicals or various radiations can cause the appearance of new traits in plant organisms, the so-called mutations. They can occur in a living organism and spontaneously. In this case, the most likely causes of mutations are changes in the physiological and biochemical processes occurring in the cell itself. They are usually caused as a result of changes in external conditions. Studies of spontaneous mutagenesis have shown that all the regularities characteristic of it can be applied to induced mutagenesis as well.

One of the promising methods for obtaining artificial mutations is radiation. Radiation selection makes it possible to obtain a significant number of useful mutants in a relatively short time - about 20% of the total number of new forms. In addition, radiation makes it possible to influence individual traits of a whole plant without changing others that are economically useful, which cannot be achieved by any other methods.

The founders of radiation genetics are G.A. Nadson, G.S. Filippov, who in 1925 studied the effect of ionizing radiation on the hereditary variability of yeast.

In 1930, there was an active growth in research in the field of obtaining radiomutants for a number of agricultural crops in our country. So, A.A. Sapegin, L.N. Delone carried out a series of fundamental works on wheat breeding. They also covered some questions of the dependence of mutations on the dose rate of radiation, the physiological state of the organism before irradiation, and so on. The question arose about the radiomutability of various plant species, about the frequency of mutations of individual genes. A. N. Lutkov found that under γ-irradiation, mutations are most often observed in the genes that regulate the development of vegetative organs, and the genes responsible for the formation of flower organs have undergone less change.

Large theoretical developments in the problem of the gene and structural disorders of the chromosomal apparatus as a result of exposure to the cell with a radioisotope were carried out by A.S. Serebrovsky and N.P. Dubinin.

By 1940, researches on radiation genetics, which had been actively started in our country, were practically stopped by 1940. Entire schools of geneticists and breeders were expelled from science as a result of the activities of T.D. Lysenko.

During this period, abroad, especially in Sweden, the USA, Japan and other countries, new research and production associations equipped with modern technology were created. The results obtained by them were very significant. The bred new varieties and hybrids of many agricultural crops gave large yield increases, were more resistant to diseases, and were technologically advanced in production.

All this led to the fact that in the early - mid-1950s the theory of genetic heredity was officially recognized in the USSR, and its supporters I.P. Dubinin, P.K. Shkvarnikov, S.S. Alikhanyan, A.M. Kuzin and others got the opportunity to resume their research on solving the problems of radiation genetics and selection, studying the effects of various sources of radiation on the cell, as the basis and root cause of all subsequent changes in the body.

In the 1960s. the leading countries have already released 7 varieties of mutant origin, in 1970 - 80, in 1975 - about 120, and at present more than 200 varieties of different crops have been registered that have more economically valuable properties compared to previously known varieties. Such significant results were achieved by foreign researchers to a large extent not only through the use of radiation mutagenesis alone, but also its rational combination with chemical mutagenesis. They developed both of these directions, not opposing them to each other, but mutually enriching, and this despite the fact that the priority of chemical mutagenesis belongs to our domestic researchers - V.V. Sakharov, K.F. Magrzhikovskaya, V.P. Ponomarev, I.A. . Rapoport and others.

The main goal of radiation selection- get a lot of variety

artificial mutants, which is unattainable either in natural conditions or when using

chemical mutagens. During radiation mutagenesis, most of the signs that appeared

are unfavorable. Often as a result radiation exposure appear

chimeric (ugly) and oppressed forms. However, due to duplications (change

chromosome, in which one of its sections is linearly represented two or more times)

there is a certain probability of occurrence of beneficial features, such as high

yield, modified chemical composition(e.g. high protein content),

early maturity, resistance to lodging, cold and high temperature, diseases, etc.

(Fokin et al., 2005).

Relatively high radiation doses are required to obtain mutant plants. AT

In radiation genetics, in addition to lethal, a critical dose of radiation is distinguished.

A critical dose is such a dose at which a strong inhibition of organisms is observed, but

a significant part of them still survive and give a large number of mutations. The cell nucleus is more

sensitive to radiation than the cytoplasm. It can be affected at a dose equal to just

several x-rays, while the cytoplasm is able to tolerate large doses. Difference

in the radiosensitivity of the nucleus and cytoplasm can reach a value of 100,000 times or more.

(Gulyaev, 1984). Currently, critical doses have been established for more than 150

cultivated and many species of wild plants. Their critical doses ranged from 400 to 200

000R (Table 5).

Usually, large quantity mutations can be obtained at sublethal doses -

doses that cause death in about 50 and even 70% of plants. Usually manifested

the following pattern: the higher the dose, the greater the number of mutations appears, but with

the death of organisms is higher. At low doses, the repair processes have time to take place even in

the time of exposure and the appearance of mutations are unlikely; at high doses, on the contrary, substances

inducing changes prevail over repair enzymes. To obtain mutations, seeds, pollen, seedlings, various

plant organs (including reproductive organs) different stages organogenesis or whole

plants. Seed irradiation is most often used. Important radiation exposure factors - type

radiation, the dose and its power, the phase of plant development or the condition of the seeds. With internal

irradiation of seeds, they are soaked in solutions of radioactive substances. Mutations are obtained with

growing plants in vegetation vessels on a nutrient medium with the addition of

radionuclides. For irradiation, radiation from short-lived radioisotopes is usually used.

Mutants with economically useful properties rarely occur. AT

in most cases, they are not finished varieties, but represent only the original

selection material. There are two main ways of selective use

artificial mutations:

direct use of mutations obtained from the best released varieties;

use of mutations in the process of hybridization.

In the first case, the task is to improve existing varieties for some

economic and biological characteristics, correcting their individual shortcomings. This method

considered promising in breeding for disease resistance. Direct method

the use of mutations is designed for the rapid creation of source material with the desired

signs and properties. However, with the high demands placed on modern

breeding varieties, this method rarely gives the desired results. Received

due to mutagenesis, the starting material is usually used in the process

hybridization.

Thus, the creation of new varieties of cultivated plants under the influence of

ionizing radiation consists of two stages. At the first stage, it is induced

the emergence of the maximum possible number of modified plants. The second stage is

creation of new plant varieties by conventional methods of traditional breeding. On different

stages of ontogenesis, various mutations can appear, which can subsequently

turn out to be favorable. In the first generation, as a rule, chimeric

(ugly) forms, a more accurate idea of the output of mutations gives the second generation.

When growing cross-pollinated plants from irradiated seeds in the first

generation requires their strict isolation from other plants to prevent pollination;

otherwise, the mutation is easily lost.

The frequency and spectrum of mutations induced by certain mutagens in a given

object, can be significantly changed, i.e. modify. This is achieved by changing

mutagenic treatment regimen or application before, during or after exposure to certain

some plants, it was found that the effect of ionizing radiation to a large extent

depends on whether it is carried out in the presence of oxygen or without it. It turned out that

an oxygen-free environment is a protective agent against ionization, while irradiation in

atmosphere of pure oxygen dramatically increases the percentage of mutations (oxygen effect).

It turned out that after irradiation, an increase in oxygen in the environment enhances the damaging

the effect of ionization, while in an oxygen-free environment is noticeably weakened (Gulyaev, 1984).

Currently, more than 1000 varieties of cultivated plants obtained

method of induced mutations, grown around the world on an area of several

million hectares. Radiation selection methods have been used to obtain a significant number of new

valuable varieties of cereals and other crops - mustard, rapeseed, tomatoes, ornamental crops. AT

a number of countries grow high-yielding peas and barley, which gives a strong straw.

High-yielding, rust-resistant, non-lodging oats with

short stem. Forms of wheat and barley with high resistance to stem and leaf rust have been obtained. In our country, economically valuable mutants have been obtained from

wheat: non-lodging, more productive, high protein, resistant

to fungal diseases of the form (Faitelberg-Blank et al., 1974).

Radiation mutagenesis radiation mutagenesis- radiation mutagenesis.

Obtaining mutations under the influence of ionizing radiation<ionizing radiation>; distinguish spontaneous (natural) R.m.- under the influence of solar (cosmic) radiation or radiation not controlled by humans (underground fossils, etc.), and artificial (induced, directed) R.m. under human controlled (usually experimental) conditions; second type R.m. is widely used in breeding (especially in plant breeding) to obtain a wide range of different mutations, among which useful ones can be selected.

(Source: "English-Russian Explanatory Dictionary of Genetic Terms". Arefiev V.A., Lisovenko L.A., Moscow: VNIRO Publishing House, 1995)

See what "radiation mutagenesis" is in other dictionaries:

Radiation mutagenesis- * radiaton mutagenesis * radiaton mutagenesis ...

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See Genetic Action of Radiations. * * * RADIATION MUTAGENESIS RADIATION MUTAGENESIS, see Genetic action of radiations (see GENETIC ACTION OF RADIATIONS) ... encyclopedic Dictionary

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